This invention relates to apparatus and methods for reducing the width of plastics pipes, and more particularly to such apparatus and methods for reducing temporarily the width of plastics liner pipes for use in relining old or damaged fluid transport pipelines, such as mains water or drainage water pipelines.
The provision of such plastics liner pipes in these circumstances is a known area of technology utilising a variety of ways of fitting the liner pipes into the existing pipework system. The present invention relates to a technique, hereinafter referred to as the "roll-down" technique, in which a liner pipe, either in a continuous length as formed on extrusion, or as separate plastics pipes butt-welded together to a continuous length, and having an appropriate width for eventually fitting tightly within the pipeline to be relined is pushed through a sequence of roller sets to reduce the width of the liner temporarily so that it may then be fed into and through the pipeline system to be relined and subsequently allowed to expand, possibly with the help of pressurised fluids and/or heat, to its original width so as to fit tightly within the original pipework.
In such a roll down system, the pipe liner is physically driven from the upstream end through a succession of curved profile rolls each of which, in end view, is somewhat half-circular in configuration, the basic principle being that the pipe liner, of larger diameter than a first pair of opposed rolls having a somewhat circular roll throat in front view, is, subject to the thrusting force from upstream, caused to reduce in diameter on passage through that set of rolls, and then on through a second pair of rolls, usually rotatable at right angles to the first set of rolls, and possibly even a third pair of rolls, again having their axes of rotation at right angles to the previous set of rolls.
It has been found in such an arrangement that a straightforward reduction in diameter of the liner pipe in passing through a set of such rolls, if the rolls exert a truly circular radial force on the incoming pipes, and therefore result in the output of a truly circular reduced pipe from the first rolls, can result in collapse of the pipe liner during passage therethrough inwardly into a configuration generally known as a "heart collapse" (from its collapsed configuration of a somewhat heart-shaped nature). When this occurs, there is quite clearly a failure of the rolling technique.